Message mapping via frequency and/or time indexing

ABSTRACT

This disclosure relates to techniques for supporting message mapping via time and/or frequency indexing. For example, these techniques may be applied to device-to-device wireless communication. For example, device to device discovery may use message mapping via frequency indexing. A portion of the payload of a message, such as a discovery message, may be offloaded to a frequency and/or time index. A receiving device may determine the offloaded portion of the payload based on the frequency and/or time (e.g., subcarrier and/or slot) used to transmit the message.

PRIORITY CLAIM

This application is a continuation of U.S. patent application Ser. No.16/391,559, entitled “Message Mapping via Frequency and/or TimeIndexing,” filed Apr. 23, 2019, which claims priority to U.S.provisional patent application Ser. No. 62/664,848, entitled “MessageMapping via Frequency Indexing,” filed Apr. 30, 2018 and to U.S.provisional patent application Ser. No. 62/737,966, entitled “MessageMapping via Frequency Indexing,” filed Sep. 28, 2018, each of which ishereby incorporated by reference in its entirety as though fully andcompletely set forth herein. The claims in the instant application aredifferent than those of the parent application or other relatedapplications. The Applicant therefore rescinds any disclaimer of claimscope made in the parent application or any predecessor application inrelation to the instant application. The Examiner is therefore advisedthat any such previous disclaimer and the cited references that it wasmade to avoid, may need to be revisited. Further, any disclaimer made inthe instant application should not be read into or against the parentapplication or other related applications.

TECHNICAL FIELD

The present application relates to wireless communication, including toschemes for message mapping via frequency indexing that could be usedfor device-to-device wireless communications.

DESCRIPTION OF THE RELATED ART

Wireless communication systems are rapidly growing in usage. Further,wireless communication technology has evolved from voice-onlycommunications to also include the transmission of data, such asInternet and multimedia content.

Mobile electronic devices may take the form of smart phones or tabletsthat a user typically carries. Wearable devices (also referred to asaccessory devices) are a newer form of mobile electronic device, oneexample being smart watches. Additionally, low-cost low-complexitywireless devices intended for stationary or nomadic deployment are alsoproliferating as part of the developing “Internet of Things”. In otherwords, there is an increasingly wide range of desired devicecomplexities, capabilities, traffic patterns, and other characteristics.One new feature is device-to-device (D2D) communication, in whichdevices must perform discovery. Discovery messaging between devices mayincur signaling overhead. Such discovery messaging may requirerelatively high coding rates, thus negatively impacting decodingperformance. In general, it would be desirable to recognize and provideimproved support for a broad range of desired wireless communicationcharacteristics. Therefore, improvements in the field are desired.

SUMMARY

Embodiments are presented herein of, inter alia, systems, apparatuses,and methods for using a frequency (e.g., subcarrier) index and/or time(e.g., slot) index to convey certain information. One exemplaryapplication may be performing synchronization using frequency indexingas part of narrowband device-to-device wireless communications. Theinformation carried by indexing (whether in frequency and/or time) maybe part of the overall payload of a message and/or part of preambleidentification (e.g., in discovery).

As noted above, the number of use cases for different classes ofwireless devices with widely variable capabilities and usageexpectations are growing. While many wireless communication systemsprimarily utilize infrastructure mode type communications, e.g., inwhich one or more base stations and potentially a supporting network areused as intermediaries between endpoint devices, one possible use casefor wireless communication includes direct device-to-device (D2D)communications. This disclosure presents various techniques forsupporting such communications, including features and techniques forperforming device-to-device discovery using message mapping viafrequency indexing. In other words, at least some information may beconveyed via selection of a specific frequency or frequency range (e.g.,subcarrier) for discovery messaging. These techniques may reducesignaling overhead for D2D discovery communications and/or may improvedecoding performance (e.g., by allowing lower coding rates). Further,design features of an exemplary discovery message are presented. Similartechniques and design features may also be applied in a time index basedmapping scheme.

The techniques described herein may be implemented in and/or used with anumber of different types of devices, including but not limited tocellular phones, tablet computers, accessory and/or wearable computingdevices, portable media players, cellular base stations and othercellular network infrastructure equipment, servers, and any of variousother computing devices.

This summary is intended to provide a brief overview of some of thesubject matter described in this document. Accordingly, it will beappreciated that the above-described features are merely examples andshould not be construed to narrow the scope or spirit of the subjectmatter described herein in any way. Other features, aspects, andadvantages of the subject matter described herein will become apparentfrom the following Detailed Description, Figures, and Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present subject matter can be obtainedwhen the following detailed description of the embodiments is consideredin conjunction with the following drawings.

FIG. 1 illustrates an example wireless communication system including anaccessory device, according to some embodiments;

FIG. 2 illustrates an example wireless communication system in which twowireless devices can perform direct device-to-device communication,according to some embodiments;

FIG. 3 is a block diagram illustrating an example wireless device,according to some embodiments;

FIG. 4 is a block diagram illustrating an example base station,according to some embodiments;

FIG. 5 is a communication flow diagram illustrating an exemplary methodfor performing device-to-device wireless discovery communications usingmessage mapping via frequency indexing, according to some embodiments;

FIG. 6 illustrates possible timing of various aspects of an exemplarypossible framework for device-to-device wireless discoverycommunications using message mapping via frequency indexing, accordingto some embodiments;

FIGS. 7-9 illustrate various elements of discovery message design fordevice-to-device wireless discovery communications using message mappingvia frequency indexing, according to some embodiments;

FIGS. 10-13 illustrate examples of possible device-to-device wirelesscommunications using message mapping via frequency indexing in the caseof peer-to-peer (P2P) discovery, according to some embodiments;

FIGS. 14-17 illustrate examples of possible device-to-device wirelesscommunications using message mapping via frequency indexing in the caseof presence discovery, according to some embodiments;

FIGS. 18-19 illustrate examples of possible benefits of reducingdiscovery message payload, according to some embodiments;

FIG. 20 illustrates a method for operating a receiving device, accordingto some embodiments;

FIG. 21 illustrates an exemplary design of a discovery message,according to some embodiments;

FIG. 22 illustrates a method for coding and decoding a discoverymessage, according to some embodiments;

FIG. 23 illustrates exemplary channel estimation techniques, accordingto some embodiments;

FIG. 24 illustrates exemplary carrier frequency refinement techniques,according to some embodiments;

FIGS. 25-53 illustrate exemplary simulation results, according to someembodiments; and

FIGS. 54 and 55 illustrate an exemplary mapping scheme.

While the features described herein are susceptible to variousmodifications and alternative forms, specific embodiments thereof areshown by way of example in the drawings and are herein described indetail. It should be understood, however, that the drawings and detaileddescription thereto are not intended to be limiting to the particularform disclosed, but on the contrary, the intention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the subject matter as defined by the appended claims.

DETAILED DESCRIPTION Acronyms

The following acronyms are used in the present disclosure.

3GPP: Third Generation Partnership Project

3GPP2: Third Generation Partnership Project 2

GSM: Global System for Mobile Communications

UMTS: Universal Mobile Telecommunications System

LTE: Long Term Evolution

NR: New Radio

OGRS: Off Grid Radio Service

IoT: Internet of Things

NB: Narrowband

D2D: device-to-device

OOC: out-of-coverage

Terminology

The following are definitions of terms used in this disclosure:

Memory Medium—Any of various types of non-transitory memory devices orstorage devices. The term “memory medium” is intended to include aninstallation medium, e.g., a CD-ROM, floppy disks, or tape device; acomputer system memory or random access memory such as DRAM, DDR RAM,SRAM, EDO RAM, Rambus RAM, etc.; a non-volatile memory such as a Flash,magnetic media, e.g., a hard drive, or optical storage; registers, orother similar types of memory elements, etc. The memory medium mayinclude other types of non-transitory memory as well or combinationsthereof. In addition, the memory medium may be located in a firstcomputer system in which the programs are executed, or may be located ina second different computer system which connects to the first computersystem over a network, such as the Internet. In the latter instance, thesecond computer system may provide program instructions to the firstcomputer for execution. The term “memory medium” may include two or morememory mediums which may reside in different locations, e.g., indifferent computer systems that are connected over a network. The memorymedium may store program instructions (e.g., embodied as computerprograms) that may be executed by one or more processors.

Carrier Medium—a memory medium as described above, as well as a physicaltransmission medium, such as a bus, network, and/or other physicaltransmission medium that conveys signals such as electrical,electromagnetic, or digital signals.

Programmable Hardware Element—includes various hardware devicescomprising multiple programmable function blocks connected via aprogrammable interconnect. Examples include FPGAs (Field ProgrammableGate Arrays), PLDs (Programmable Logic Devices), FPOAs (FieldProgrammable Object Arrays), and CPLDs (Complex PLDs). The programmablefunction blocks may range from fine grained (combinatorial logic or lookup tables) to coarse grained (arithmetic logic units or processorcores). A programmable hardware element may also be referred to as“reconfigurable logic”.

Computer System—any of various types of computing or processing systems,including a personal computer system (PC), mainframe computer system,workstation, network appliance, Internet appliance, personal digitalassistant (PDA), television system, grid computing system, or otherdevice or combinations of devices. In general, the term “computersystem” can be broadly defined to encompass any device (or combinationof devices) having at least one processor that executes instructionsfrom a memory medium.

User Equipment (UE) (or “UE Device”)—any of various types of computersystems or devices that are mobile or portable and that perform wirelesscommunications. Examples of UE devices include mobile telephones orsmart phones (e.g., iPhone™, Android™-based phones), portable gamingdevices (e.g., Nintendo DS™, PlayStation Portable™, Gameboy Advance™,iPhone™), laptops, wearable devices (e.g. smart watch, smart glasses),PDAs, portable Internet devices, music players, data storage devices, orother handheld devices, etc. In general, the term “UE” or “UE device”can be broadly defined to encompass any electronic, computing, and/ortelecommunications device (or combination of devices) which is easilytransported by a user and capable of wireless communication.

Wireless Device—any of various types of computer systems or devices thatperform wireless communications. A wireless device can be portable (ormobile) or may be stationary or fixed at a certain location. A UE is anexample of a wireless device.

Communication Device—any of various types of computer systems or devicesthat perform communications, where the communications can be wired orwireless. A communication device can be portable (or mobile) or may bestationary or fixed at a certain location. A wireless device is anexample of a communication device. A UE is another example of acommunication device.

Base Station—The term “Base Station” (also called “eNB”) has the fullbreadth of its ordinary meaning, and at least includes a wirelesscommunication station installed at a fixed location and used tocommunicate as part of a wireless cellular communication system.

Link Budget Limited—includes the full breadth of its ordinary meaning,and at least includes a characteristic of a wireless device (e.g., a UE)which exhibits limited communication capabilities, or limited power,relative to a device that is not link budget limited, or relative todevices for which a radio access technology (RAT) standard has beendeveloped. A wireless device that is link budget limited may experiencerelatively limited reception and/or transmission capabilities, which maybe due to one or more factors such as device design, device size,battery size, antenna size or design, transmit power, receive power,current transmission medium conditions, and/or other factors. Suchdevices may be referred to herein as “link budget limited” (or “linkbudget constrained”) devices. A device may be inherently link budgetlimited due to its size, battery power, and/or transmit/receive power.For example, a smart watch that is communicating over LTE or LTE-A witha base station may be inherently link budget limited due to its reducedtransmit/receive power and/or reduced antenna. Wearable devices, such assmart watches, are generally link budget limited devices. Alternatively,a device may not be inherently link budget limited, e.g., may havesufficient size, battery power, and/or transmit/receive power for normalcommunications over LTE or LTE-A, but may be temporarily link budgetlimited due to current communication conditions, e.g., a smart phonebeing at the edge of a cell, etc. It is noted that the term “link budgetlimited” includes or encompasses power limitations, and thus a powerlimited device may be considered a link budget limited device.

Processing Element (or Processor)—refers to various elements orcombinations of elements. Processing elements include, for example,circuits such as an ASIC (Application Specific Integrated Circuit),portions or circuits of individual processor cores, entire processorcores, individual processors, programmable hardware devices such as afield programmable gate array (FPGA), and/or larger portions of systemsthat include multiple processors.

Automatically—refers to an action or operation performed by a computersystem (e.g., software executed by the computer system) or device (e.g.,circuitry, programmable hardware elements, ASICs, etc.), without userinput directly specifying or performing the action or operation. Thusthe term “automatically” is in contrast to an operation being manuallyperformed or specified by the user, where the user provides input todirectly perform the operation. An automatic procedure may be initiatedby input provided by the user, but the subsequent actions that areperformed “automatically” are not specified by the user, i.e., are notperformed “manually”, where the user specifies each action to perform.For example, a user filling out an electronic form by selecting eachfield and providing input specifying information (e.g., by typinginformation, selecting check boxes, radio selections, etc.) is fillingout the form manually, even though the computer system must update theform in response to the user actions. The form may be automaticallyfilled out by the computer system where the computer system (e.g.,software executing on the computer system) analyzes the fields of theform and fills in the form without any user input specifying the answersto the fields. As indicated above, the user may invoke the automaticfilling of the form, but is not involved in the actual filling of theform (e.g., the user is not manually specifying answers to fields butrather they are being automatically completed). The presentspecification provides various examples of operations beingautomatically performed in response to actions the user has taken.

Configured to—Various components may be described as “configured to”perform a task or tasks. In such contexts, “configured to” is a broadrecitation generally meaning “having structure that” performs the taskor tasks during operation. As such, the component can be configured toperform the task even when the component is not currently performingthat task (e.g., a set of electrical conductors may be configured toelectrically connect a module to another module, even when the twomodules are not connected). In some contexts, “configured to” may be abroad recitation of structure generally meaning “having circuitry that”performs the task or tasks during operation. As such, the component canbe configured to perform the task even when the component is notcurrently on. In general, the circuitry that forms the structurecorresponding to “configured to” may include hardware circuits.

Various components may be described as performing a task or tasks, forconvenience in the description. Such descriptions should be interpretedas including the phrase “configured to.” Reciting a component that isconfigured to perform one or more tasks is expressly intended not toinvoke 35 U.S.C. § 112, paragraph six, interpretation for thatcomponent.

FIGS. 1-2—Wireless Communication System

FIG. 1 illustrates an example of a wireless cellular communicationsystem. It is noted that FIG. 1 represents one possibility among many,and that features of the present disclosure may be implemented in any ofvarious systems, as desired. For example, embodiments described hereinmay be implemented in any type of wireless device.

As shown, the exemplary wireless communication system includes acellular base station 102, which communicates over a transmission mediumwith one or more wireless devices 106A, 106B, etc., as well as accessorydevice 107. Wireless devices 106A, 106B, and 107 may be user devices,which may be referred to herein as “user equipment” (UE) or UE devices.

The base station 102 may be a base transceiver station (BTS) or cellsite, and may include hardware that enables wireless communication withthe UE devices 106A, 106B, and 107. The base station 102 may also beequipped to communicate with a network 100 (e.g., a core network of acellular service provider, a telecommunication network such as a publicswitched telephone network (PSTN), and/or the Internet, among variouspossibilities). Thus, the base station 102 may facilitate communicationamong the UE

devices 106 and 107 and/or between the UE devices 106/107 and thenetwork 100. In other implementations, base station 102 can beconfigured to provide communications over one or more other wirelesstechnologies, such as an access point supporting one or more WLANprotocols, such as 802.11a, b, g, n, ac, ad, and/or ax, or LTE in anunlicensed band (LAA).

The communication area (or coverage area) of the base station 102 may bereferred to as a “cell.” The base station 102 and the UEs 106/107 may beconfigured to communicate over the transmission medium using any ofvarious radio access technologies (RATs) or wireless communicationtechnologies, such as GSM, UMTS (WCDMA, TDS-CDMA), LTE, LTE-Advanced(LTE-A), NR, Off-grid radio service (OGRS), HSPA, 3GPP2 CDMA2000 (e.g.,1xRTT, 1xEV-DO, HRPD, eHRPD), Wi-Fi, etc.

Base station 102 and other similar base stations (not shown) operatingaccording to one or more cellular communication technologies may thus beprovided as a network of cells, which may provide continuous or nearlycontinuous overlapping service to UE devices 106A-N and 107 and similardevices over a geographic area via one or more cellular communicationtechnologies.

Note that at least in some instances a UE device 106/107 may be capableof communicating using any of multiple wireless communicationtechnologies. For example, a UE device 106/107 might be configured tocommunicate using one or more of GSM, UMTS, CDMA2000, LTE, LTE-A, NR,OGRS, WLAN, Bluetooth, one or more global navigational satellite systems(GNSS, e.g., GPS or GLONASS), one and/or more mobile televisionbroadcasting standards (e.g., ATSC-M/H), etc. Other combinations ofwireless communication technologies (including more than two wirelesscommunication technologies) are also possible. Likewise, in someinstances a UE device 106/107 may be configured to communicate usingonly a single wireless communication technology.

The UEs 106A and 106B may include handheld devices such as smart phonesor tablets, and/or may include any of various types of device withcellular communications capability. For example, one or more of the UEs106A and 106B may be a wireless device intended for stationary ornomadic deployment such as an appliance, measurement device, controldevice, etc. The UE 106B may be configured to communicate with the UEdevice 107, which may be referred to as an accessory device 107. Theaccessory device 107 may be any of various types of wireless devices,typically a wearable device that has a smaller form factor, and may havelimited battery, output power and/or communications abilities relativeto UEs 106. As one common example, the UE 106B may be a smart phonecarried by a user, and the accessory device 107 may be a smart watchworn by that same user. The UE 106B and the accessory device 107 maycommunicate using any of various short range communication protocols,such as Bluetooth or Wi-Fi.

The UE 106B may also be configured to communicate with the UE 106A. Forexample, the UE 106A and UE 106B may be capable of performing directdevice-to-device (D2D) communication. The D2D communication may besupported by the cellular base station 102 (e.g., the BS 102 mayfacilitate discovery, among various possible forms of assistance), ormay be performed in a manner unsupported by the BS 102. For example,according to at least some aspects of this disclosure, the UE 106A andUE 106B may be capable of arranging and performing narrowband D2Dcommunication with each other even when out-of-coverage of the BS 102and other cellular base stations.

FIG. 2 illustrates example UE devices 106A, 106B in D2D communicationwith each other. The UE devices 106A, 106B may each be any of a mobilephone, a tablet, or any other type of hand-held device, a smart watch orother wearable device, a media player, a computer, a laptop or virtuallyany type of wireless device.

The UEs 106A, 106B may each include a device or integrated circuit forfacilitating cellular communication, referred to as a cellular modem.The cellular modem may include one or more processors (processingelements) and various hardware components as described herein. The UEs106A, 106B may each perform any of the method embodiments describedherein by executing instructions on one or more programmable processors.Alternatively, or in addition, the one or more processors may be one ormore programmable hardware elements such as an FPGA (field-programmablegate array), or other circuitry, that is configured to perform any ofthe method embodiments described herein, or any portion of any of themethod embodiments described herein. The cellular modem described hereinmay be used in a UE device as defined herein, a wireless device asdefined herein, or a communication device as defined herein. Thecellular modem described herein may also be used in a base station orother similar network side device.

The UEs 106A, 106B may include one or more antennas for communicatingusing two or more wireless communication protocols or radio accesstechnologies. In some embodiments, one or both of the UE 106A or UE 106Bmight be configured to communicate using a single shared radio. Theshared radio may couple to a single antenna, or may couple to multipleantennas (e.g., for MIMO) for performing wireless communications.Alternatively, the UE 106A and/or UE 106B may include two or moreradios. Other configurations are also possible.

FIG. 3—Block Diagram of a UE Device

FIG. 3 illustrates one possible block diagram of an UE device, such asUE device 106 or 107. As shown, the UE device 106/107 may include asystem on chip (SOC) 300, which may include portions for variouspurposes. For example, as shown, the SOC 300 may include processor(s)302 which may execute program instructions for the UE device 106/107,and display circuitry 304 which may perform graphics processing andprovide display signals to the display 360. The SOC 300 may also includemotion sensing circuitry 370 which may detect motion of the UE 106, forexample using a gyroscope, accelerometer, and/or any of various othermotion sensing components. The processor(s) 302 may also be coupled tomemory management unit (MMU) 340, which may be configured to receiveaddresses from the processor(s) 302 and translate those addresses tolocations in memory (e.g., memory 306, read only memory (ROM) 350, flashmemory 310). The MMU 340 may be configured to perform memory protectionand page table translation or set up. In some embodiments, the MMU 340may be included as a portion of the processor(s) 302.

As shown, the SOC 300 may be coupled to various other circuits of the UE106/107. For example, the UE 106/107 may include various types of memory(e.g., including NAND flash 310), a connector interface 320 (e.g., forcoupling to a computer system, dock, charging station, etc.), thedisplay 360, and wireless communication circuitry 330 (e.g., for LTE,LTE-A, NR, OGRS, CDMA2000, Bluetooth, Wi-Fi, NFC, GPS, etc.).

The UE device 106/107 may include at least one antenna, and in someembodiments multiple antennas 335 a and 335 b, for performing wirelesscommunication with base stations and/or other devices. For example, theUE device 106/107 may use antennas 335 a and 335 b to perform thewireless communication. As noted above, the UE device 106/107 may insome embodiments be configured to communicate wirelessly using aplurality of wireless communication standards or radio accesstechnologies (RATs).

The wireless communication circuitry 330 may include Wi-Fi Logic 332, aCellular Modem 334, and Bluetooth Logic 336. The Wi-Fi Logic 332 is forenabling the UE device 106/107 to perform Wi-Fi communications on an802.11 network. The Bluetooth Logic 336 is for enabling the UE device106/107 to perform Bluetooth communications. The cellular modem 334 maybe a lower power cellular modem capable of performing cellularcommunication according to one or more cellular communicationtechnologies.

As described herein, UE 106/107 may include hardware and softwarecomponents for implementing embodiments of this disclosure. For example,one or more components of the wireless communication circuitry 330(e.g., cellular modem 334) of the UE device 106/107 may be configured toimplement part or all of the methods described herein, e.g., by aprocessor executing program instructions stored on a memory medium(e.g., a non-transitory computer-readable memory medium), a processorconfigured as an FPGA (Field Programmable Gate Array), and/or usingdedicated hardware components, which may include an ASIC (ApplicationSpecific Integrated Circuit).

FIG. 4—Block Diagram of a Base Station

FIG. 4 illustrates an example block diagram of a base station 102,according to some embodiments. It is noted that the base station of FIG.4 is merely one example of a possible base station. As shown, the basestation 102 may include processor(s) 404 which may execute programinstructions for the base station 102. The processor(s) 404 may also becoupled to memory management unit (MMU) 440, which may be configured toreceive addresses from the processor(s) 404 and translate thoseaddresses to locations in memory (e.g., memory 460 and read only memory(ROM) 450) or to other circuits or devices.

The base station 102 may include at least one network port 470. Thenetwork port 470 may be configured to couple to a telephone network andprovide a plurality of devices, such as UE devices 106/107, access tothe telephone network as described above in FIGS. 1 and 2 .

The network port 470 (or an additional network port) may also oralternatively be configured to couple to a cellular network, e.g., acore network of a cellular service provider. The core network mayprovide mobility related services and/or other services to a pluralityof devices, such as UE devices 106/107. For example, the core networkmay include a mobility management entity (MME), e.g., for providingmobility management services, a serving gateway (SGW) and/or packet datanetwork gateway (PGW), e.g., for providing external data connectionssuch as to the Internet, etc. In some cases, the network port 470 maycouple to a telephone network via the core network, and/or the corenetwork may provide a telephone network (e.g., among other UE devicesserviced by the cellular service provider).

The base station 102 may include at least one antenna 434, and possiblymultiple antennas. The antenna(s) 434 may be configured to operate as awireless transceiver and may be further configured to communicate withUE devices 106/107 via radio 430. The antenna(s) 434 communicates withthe radio 430 via communication chain 432. Communication chain 432 maybe a receive chain, a transmit chain or both. The radio 430 may beconfigured to communicate via various wireless communication standards,including, but not limited to, LTE, LTE-A, NR, OGRS, GSM, UMTS,CDMA2000, Wi-Fi, etc.

The base station 102 may be configured to communicate wirelessly usingmultiple wireless communication standards. In some instances, the basestation 102 may include multiple radios, which may enable the basestation 102 to communicate according to multiple wireless communicationtechnologies. For example, as one possibility, the base station 102 mayinclude an LTE radio for performing communication according to LTE aswell as a Wi-Fi radio for performing communication according to Wi-Fi.In such a case, the base station 102 may be capable of operating as bothan LTE base station and a Wi-Fi access point. As another possibility,the base station 102 may include a multi-mode radio which is capable ofperforming communications according to any of multiple wirelesscommunication technologies (e.g., LTE and Wi-Fi, LTE and UMTS, LTE andCDMA2000, UMTS and GSM, etc.).

As described further subsequently herein, the BS 102 may includehardware and software components for implementing or supportingimplementation of features described herein. For example, while many ofthe features described herein relate to device-to-device communicationthat can be performed by UE devices without relying on an intermediarybase station, a cellular base station may be configured to also becapable of performing device-to-device communication in accordance withthe features described herein. As another possibility, the BS 102 may beinstrumental in configuring a UE 106 to perform narrowbanddevice-to-device communication according to the features describedherein, and/or certain features described herein may be performed or notperformed by a device based at least in part on whether there is a BS102 providing cellular service within range of the device. According tosome embodiments, the processor 404 of the base station 102 may beconfigured to implement part or all of the methods described herein,e.g., by executing program instructions stored on a memory medium (e.g.,a non-transitory computer-readable memory medium). Alternatively, theprocessor 404 may be configured as a programmable hardware element, suchas an FPGA (Field Programmable Gate Array), or as an ASIC (ApplicationSpecific Integrated Circuit), or a combination thereof. Alternatively(or in addition) the processor 404 of the BS 102, in conjunction withone or more of the other components 430, 432, 434, 440, 450, 460, 470may be configured to implement or support implementation of part or allof the features described herein.

FIG. 5—Communication Flow Diagram

In D2D communication, a preamble approach may be used for discovery, atleast as one possibility. The discovery procedure may consist of twoparts: preamble detection and discovery message (e.g., including msg1and msg2) decoding. It may be possible to infer some discoveryinformation from detection of the preamble sequence, e.g., part of thediscovery receiver (DR) identifier (ID). However, some discoveryinformation (e.g., discovery initiator (DI) ID) may not be inferred fromthe preamble, and may be sent via discovery message (e.g., msg1 andmsg2). Msg1 and msg2 may be transmitted via a selected subcarrier amonga set of subcarriers. Reducing the size of msg1 and msg2 may reducesignaling overhead associated with discovery, and may therefore benefitdevices performing D2D communications as well as the wireless systemmore generally. For example, due to a reduced size of the msg1 and/ormsg2, the devices may use lower coding rates to transmit and receive themessages. Thus, decoding performance may be improved.

FIG. 5 is a communication flow diagram illustrating a method forperforming discovery as part of device-to-device wirelesscommunications, according to some embodiments. In various embodiments,some of the elements of the methods shown may be performed concurrently,in a different order than shown, may be substituted for by other methodelements, or may be omitted. Additional method elements may also beperformed as desired.

Aspects of the method of FIG. 5 may be implemented by a wireless device,such as the UEs 106A-B or 107 illustrated in and described with respectto FIGS. 1-3 , or more generally in conjunction with any of the computersystems or devices shown in the above Figures, among other devices, asdesired. For example, a processor (and/or other hardware) of such adevice may be configured to cause the device to perform any combinationof the illustrated method elements and/or other method elements. Notethat while at least some elements of the method of FIG. 5 are describedin a manner relating to the use of communication techniques and/orfeatures associated with LTE, OGRS, and/or 3GPP specification documents,such description is not intended to be limiting to the disclosure, andaspects of the method of FIG. 5 may be used in any suitable wirelesscommunication system, as desired. As shown, the method may operate asfollows.

In 502, a first wireless device (e.g., UE 106A) may provide asynchronization preamble to a second wireless device (e.g., UE 106B),e.g., in accordance with a D2D wireless communication framework. Thefirst wireless device may be referred to herein as a discovery initiator(DI) and the second wireless device a discovery receiver (DR). In someembodiments, the second wireless device may be one of multiple wirelessdevices, e.g., there may be more than one DR device.

The synchronization (sync) preamble may include or otherwise imply atleast partial identification information for the intended receiver orreceivers and/or of the DI device. The sync preamble may be structuredaccording to a type of discovery that the DI is attempting to initiate.Example discovery types include peer-to-peer and presence discovery.

In peer-to-peer (P2P) discovery according to the D2D communicationframework, the sync preamble may include at least part of the (e.g.,singular) intended recipient's DR identifier (DR ID). P2P discovery mayrefer to discovery in circumstances that the DI intends to initiatecommunication with a specific DR (e.g., possibly a specific group ofDRs). Thus, the sync preamble may be used to identify the specificintended DR(s).

In presence discovery, the sync preamble may include at least part of acommon or presence DR ID. Such a common DR ID may be used incircumstances in which the DI intends to announce its presence, e.g., sothat all devices configured to utilize the D2D communication frameworkthat are in range will be aware of its presence and availability tocommunicate. The common DR ID may be known to all such devices, e.g., sothat all such devices may monitor communications associated with thecommon DR ID. In presence discovery, the sync preamble may include allor part of the ID of the DI device (DI ID). The DI ID may be associatedwith the sync preamble in addition to the common presence ID, or thecommon ID may not be associated with the sync preamble.

In some embodiments, the sync preamble may include only part of the DRand/or DI ID. Thus, the DR or DRs may need to wait for a future message(e.g., a discovery message or msg 1, described in detail below) todetermine the entire ID, e.g., the identity of the device or deviceswith which the DI intends to perform discovery.

The sync preamble may be transmitted on one or more subcarriers of aplurality of possible subcarriers. The subcarrier(s) used may beselected by any of various means. For example, the subcarrier(s) may beselected randomly, pseudo-randomly, according to a frequency hoppingscheme, or a predetermined subcarrier may be used for this purpose.

The synchronization preamble may include one or more synchronizationsequences. Each synchronization sequence may include a basis sequencethat is transmitted on a certain number of subcarriers (e.g., in thefrequency domain) and spans one or more OFDM symbols (e.g., in the timedomain). The basis sequence may be repeated multiple times. Thesynchronization sequence may further include a cover code. For example,each OFDM symbol of the synchronization sequence may be multiplied by acover bit of the cover code. As another possibility, each basis sequence(e.g., potentially including multiple OFDM symbols) may be multiplied bya cover bit of the cover code.

The synchronization sequence may be provided as part of a narrowbandD2D/P2P communication. The communication may be performed using one ormore Narrowband Internet of Things (NB-IoT) carriers, and/or may beperformed using any of various other possible (e.g., narrowband)carriers. Thus, as one possibility, the synchronization sequence may betransmitted on a carrier frequency that has a frequency width of onephysical resource block (e.g., 12 or 14 subcarriers having subcarrierspacing of 15 kHz, in some instances)

The synchronization sequence may be selected from multiple possiblesynchronization sequences. For example, multiple basis sequences may bepossible, and multiple cover codes may be possible. Each unique possiblesynchronization sequence may include a unique basis sequence among thespecified possible basis sequences combined with a unique cover codeamong the specified possible cover codes. Thus, in some instances, theremay be a large number of possible synchronization sequences.

In some instances, the synchronization sequence(s) may be selected basedat least in part on device identification information for the firstwireless device, the second wireless device, and/or a link between thefirst wireless device and the second wireless device.

The second device(s) (e.g., UE 106B) may receive and decode thesynchronization preamble.

In 504, the first device (e.g., the DI, e.g., UE 106A) may select asubcarrier to transmit a discovery message (e.g., msg 1). In otherwords, the DI may select one subcarrier (e.g., k_active) of N availablesubcarriers to use for this purpose.

In some embodiments, the subcarrier may be selected at random. In otherwords, a selected subcarrier may be selected using a function such as:k_active=uniform (0 . . . N−1). Such random selection may reduce theprobability of collision, e.g., between discovery messages transmittedby different DI devices.

In some embodiments, the subcarrier may not be selected randomly, andmay instead be selected according to a message mapping via frequencyindexing scheme, e.g., so that the subcarrier selection carries part ofthe payload of the discovery message itself. Given the random nature ofthe payload, the payload may effectively serve as a pseudo-random basisfor selecting a subcarrier. Accordingly, the collision rate may bereduced by the random (e.g., pseudo-random) selection of the subcarrier.In other words, the subcarrier may be selected based on a number of bits(e.g., K bits) of the payload of the discovery message (see also FIG. 7and associated discussion below). Thus, a DR may be able to infer the Kbits of the payload based on the identity (e.g., index) of the selectedsubcarrier. For example, the subcarrier may be selected based on the DRID, e.g., based on a part of the DR ID that was not transmitted in thesynchronization preamble. The K bits may be referred to as an offloadedportion of the payload of the discovery message, e.g., because thesebits are offloaded to the frequency indexing and thus do not need to betransmitted via channel coding, e.g., in the body of the discoverymessage. K may be greater than or equal to 1. The (e.g., maximum) numberof bits (K) that may be carried by the subcarrier selection may be equalto the logarithm (base 2) of the number of available subcarriers, e.g.,K=log₂(N).

The first device may use any one-to-one function (e.g., f) to select thesubcarrier, e.g., k_active=f(x,u).

x may represent the value decided by the K bits of the payload that iscarried by the subcarrier selection. As noted above, in some embodiments(e.g., in P2P discovery), x may be based on a part of the DR ID that wasnot transmitted in the sync preamble. Thus, the subcarrier selection mayencode/carry the information of the remainder (e.g., not previouslytransmitted bits) of the DR ID. In some embodiments (e.g., in presencediscovery), x may be based on a part of the DI ID that was nottransmitted in the sync preamble. In general, any part of the discoverymessage payload may be offloaded to subcarrier index mapping (e.g., viax), as long as that portion is sufficiently random.

u may be a variable related to other information and may be independentof the K bits of payload. For example, u may be based on frame index.One use case of u may be to perform subcarrier hopping across frames.

Various exemplary formulas for selecting subcarrier k_active aredescribed below. Note that additional formulas are possible and may beselected as desired. Among other possibilities, note that variations orcombinations of the mathematical features of these formulas arepossible. These formulas may use the following parameters:K=floor(log2(N));L=N−2^(K); and

K bits payload may be represented as: [b0 b1 . . . bK−1] (bi is either 0or 1), which has decimal value x: x=binary-to-decimal ([b0 b1 . . .bK−1]).

Example 1: k_active=mod(x, N). This example may have the advantage ofsimplicity.

Example 2: k_active=mod(x+u*L, N), where u={0: discovery message type 0,1: discovery message type 1}. For instance, discovery message type 0 maycorrespond to P2P discovery and message type 1 may correspond topresence discovery. This example may offer the benefit of reducing theoverlap between different discovery types (e.g., P2P discovery may occuron a different subset of subcarriers than presence discovery), and thusmay reduce the likelihood of collision.

Example 3: k_active=mod(x+u*L, N), where u=frame_index. Frame index maybe known to both the DI and DR devices. This example may have thebenefit of hopping through all available subcarriers over time. Thus,collision probability may be reduced. Any measure of time may be used inplace of the frame index.

Example 4: k_active =mod(x+u*L, N), where u=decimal value of prior knownDI information. This example may have the benefit of reducing overlapbetween different DIs, e.g., by adding a DI-specific subcarrier offset.Similarly, part of prior known DR information may be used. Any otherprior known information (e.g., known to both the DI and the DR) may beused. Thus, collision probability may be reduced.

Example 5: k_active=mod(x+u*L, N), where u provides an indication ofservice type, e.g., a service that is executing on the DI device and/ora service for which the DI device would like to exchange information,e.g., with one or more DR devices. More than one service may beindicated. Further, the service type indication may describe the natureof data traffic patterns for the service(s) (e.g., packet length (e.g.,mean and/or variance, etc.), packet timing (e.g., period, regularity,interval, etc.)).

Example 6: k_active=mod(x+u*L, N), where u provides an indication of thetiming accuracy level. Such an indication may inform DR devices of howaccurate the timing information available to the DI device is. Suchinformation may be useful in coordinating communications, e.g., based onframe number.

Example 7: k_active=mod(x+u*L, N), where u provides an indication of apriority order metric. Such a priority order metric may correspond tothe priority of traffic/data that the DI device wishes to exchange withone or more DR devices. For example, the priority metric may be similarto a quality of service (QoS) class indicator (QCI), e.g., the prioritymetric may be or include QCI and/or a related indicator. Further, thepriority order may indicate the urgency with which the DI device wishesto establish communication.

Example 8: k_active=mod(x+u*L, N), where u provides an indication of anidentity of the user or purpose of the DI device. For example, u mayindicate that the DI device is used for emergency services, military,etc., purposes. Alternatively, u may indicate that the DI is used by aprivate company or other specific group. Thus, the indication may alertreceiving devices in the same group of users/purposes to respond and/ormay alert other devices not to respond.

As noted above, any part of the discovery message payload may beoffloaded to subcarrier index mapping (e.g., via x), as long as thatportion is sufficiently random. In P2P discovery, DR ID may be fullyidentified upon receiving the discovery message (msg 1). Note that DR IDmay not be fully known before the discovery message, thus K bits of theDR ID may be used as input x for the subcarrier mapping function. Forexample, K bits of the most or least significant bits (e.g., MSB/LSB)(or other prior agreed part) of the unknown part of the DR ID may beselected as the payload. Alternatively, Q bits of MSB/LSB of the unknownpart (e.g., not previously transmitted) of DR ID, and (K-Q) bits may beselected from the known (e.g., previously transmitted) part of the DRID. This selection may be implemented either as a single bit or XOR of aset of bits. For example, using a single bit may allow the use ofadditional subcarriers (e.g., in the case of Q=3 bits, a fourth bit(e.g., 4−3=1 bit from the known part of the DR ID) may allow selectionbetween 2⁴=16 subcarriers, rather than 2³=8 subcarriers. Similarly,multiple bits may be used (e.g., via XOR), e.g., as u, similar toexample 4 above.

In payload mapping of a presence discovery message, the DI ID may not beknown to the DR device(s) prior to receiving the discovery message. Notethat in presence discovery, a DR may monitor a common/group presence ID,and may not know whether the DI has indicated the common ID (e.g., inthe sync preamble, e.g., indicating presence discovery or P2P discovery)before decoding the discovery message. In the case of presencediscovery, the payload may be mapped (e.g., as x) in any of variousways. In one example, K bits of the most or least significant bits(e.g., MSB/LSB) (or other prior agreed part) of the DI ID may beselected as the payload, x. In a second example, K bits of the MSB/LSB(or other prior agreed part) of the unknown part of the common/presenceID may be used. In a third example, Q bits of MSB/LSB of the unknown(e.g., not previously transmitted) part of the common/presence ID, and(K-Q) bits may be selected from the known (previously transmitted) partof the common/presence ID. This selection may be implemented either as asingle bit or XOR of a set of bits, e.g., as discussed above for P2Pdiscovery. The benefit of the second and third examples may be to reducefalse alarms of common/presence ID monitoring (e.g., reduce thefrequency that a DR device may wrongly determine that a DI is announcingpresence when the DI actually intends to perform P2P discovery).

In some embodiments, multiple subcarriers may be selected. Thus, payloadinformation may be encoded based on each of the subcarriers, and/or thecombination of subcarriers selected.

As explained in more detail below (see FIGS. 18-19 ), carrying a portionof the (e.g., complete) payload in this manner (e.g., via subcarrierindexing, e.g., offloading) may allow the wireless device (e.g., DI) toreduce the amount of the payload sent via channel coding the discoverymessage. In other words, by offloading a portion (e.g., K bits) of thecomplete payload (e.g., M bits), the DI may transmit (e.g., via channelcoding) only a remaining, non-offloaded portion (e.g., M−K bits).However, the full payload (e.g., M bits) may be reconstructed by the DR,e.g., by directly decoding the non-offloaded portion and inferring theoffloaded portion based on the frequency mapping. The reduction in thenumber of bits carried by channel coding may allow for a lower code rateand may result in better decoding performance. Additionally oralternatively, signaling overhead may be reduced.

In 506, the second device (e.g., or second devices, DR) may determinewhich, if any, subcarriers to monitor, e.g., during a period of time inwhich the DR may anticipate receiving a discovery message from the DI.The determination may be based at least in part on the synchronizationpreamble.

In some embodiments, a DR may determine to monitor a single frequency,e.g., which may correspond to its DR ID or to a common presence ID. Forexample, based on decoding the synchronization preamble, the DR maydetermine that a partial DR ID associated with the preamble maypotentially match either its DR ID or a common presence ID. Based onsuch a determination, the DR may monitor the subcarrier that correspondsto that ID, e.g., according to a message mapping via frequency indexingscheme. In other words, the DR may monitor the subcarrier that a DIwould use to indicate the ID (e.g., DR ID or presence ID) correspondingto the DR. In some embodiments, both the DR ID and separately the commonID may potentially match the partial ID associated with the preamble,and the DR may accordingly monitor both channels.

In some embodiments, e.g., based on detecting a common/presence ID inthe sync preamble, the DR may monitor all subcarriers. The DR may beable to determine payload information associated with a discoverymessage based on the subcarrier used to transmit the message.

In some embodiments, e.g., based on detecting a DR ID in the syncpreamble that does not match either the DR's DR ID or a common presenceID, the DR may not monitor any subcarriers. In other words, the DR maydetermine to sleep or enter a low power state for the period of timeassociated with the discovery message, e.g., because the sync preambleindicates that the discovery message is not intended for the DR.

In 508, the first device (DI) (e.g., UE 106A) may transmit a discoverymessage (Msg 1) to the second device(s) (DR) (e.g., UE 106B) using theselected subcarrier. As described herein, some payload information (x,e.g., the offloaded portion, e.g., including K bits) may be encoded in(e.g., indicated by) the subcarrier selection, and other payloadinformation (e.g., the non-offloaded portion, e.g., M−K bits) may betransmitted via channel coding or other techniques. The discoverymessage may include information such as DR ID and/or DI ID, amongvarious possibilities.

The DR device(s) may receive and decode the discovery message. Based onthe identity of the subcarrier used, the DR may infer the offloadedpayload information (x) indicated by the subcarrier selection. Further,the DR may decode the other (e.g., non-offloaded) payload information.Thus, based on the offloaded and non-offloaded portion of the payloadinformation, the DR may determine the complete payload of the message.

In 510, the DR device(s) (e.g., UE 106B) may respond (msg 2) to the DI(e.g., UE 106A). Any such responses may be based on the payloadinformation of the discovery message (msg 1). For example, based ondetermining that the discovery message (in combination with the syncpreamble) indicated the DR ID of the DR device (e.g., P2P discovery),the DR device may reply with msg 2 to continue P2P discovery and furthercommunication with the DI. Similarly, in the case of presence discovery,some or all DR devices may respond with identifying information (e.g.,DR ID), e.g., which may enable the DI device to send P2P discoverymessages targeted to specific DR devices in future discovery windows.

In some embodiments, the DR device(s) may not respond. For example,based on determining that a P2P discovery message is not directed to aDR device's DR ID, that DR device may not respond. Similarly, it may bethe case that no response may be necessary to a presence discoverymessage.

FIGS. 6-53—Additional information

FIGS. 6-53 and the following additional information are provided asbeing illustrative of further considerations and possible implementationdetails relating to the method of FIG. 5 and are not intended to belimiting to the disclosure as a whole. Numerous variations andalternatives to the details provided herein below are possible andshould be considered within the scope of the disclosure.

FIG. 6—Timing of D2D Communications Using Message Mapping Via FrequencyIndexing

A variety of frameworks and framework elements may be possible for D2Dwireless communication, e.g., including wide- and narrowbandimplementations, implementations that utilize a synchronization masterdevice for synchronization, and/or implementations that utilize apreamble-based approach to performing synchronization, among variouspossibilities. At least for some devices (e.g., in consideration oftheir transmit power regimes), propagation characteristics fornarrowband communications may result in greater range capacity thanwider-band communications. Note that effective communication range maybe further increased, at least in some instances, if a lower-frequencycommunication band (e.g., 900 MHz unlicensed spectrum, as onepossibility) is used for the narrowband D2D communications. As anotherpossibility, some (e.g., lower complexity) devices may be configured toperform only narrowband communications (e.g., may have RF front endlimitations, and/or may have battery limitations functionally limitingcapability to perform wider-band communications). As yet anotherpossibility, some devices, even if capable of both wideband andnarrowband communication, may prefer to perform narrowband communicationwhen possible, e.g., if the narrowband communication can reduce powerconsumption by the devices.

The techniques described herein may be used in scenarios when one ormore of the communicating wireless devices are not within communicationrange of a cellular base station (e.g., the devices may beout-of-coverage/OOC), according to some embodiments.

For example, Off Grid Radio Service (OGRS) is a system that is beingdeveloped to provide long range peer-to-peer (P2P)/D2D communication,e.g., in absence of a wide area network (WAN) or WLAN radio connectionto support a variety of possible features. At least according to someembodiments, OGRS systems may support some or all of the featurespreviously described herein with respect to FIG. 5 .

According to some embodiments, OGRS may operate in unlicensed low ISMbands, e.g., between 700 MHz and 1 GHz, for extended range purposes, andmay use one or multiple carriers of approximately 200 kHz. OGRS may bedesigned to meet the local spectrum regulatory requirements, such aschannel duty cycle, operating frequencies, hopping pattern, LBT, maximumtransmit power, and occupied bandwidth.

As one possibility for providing the physical narrowband carrier fornarrowband D2D communications, a NB-IoT carrier may be used. Accordingto some embodiments, NB-IoT carriers may be configured for use instandalone deployments (e.g., in a repurposed GSM band), guardbanddeployments (e.g., in a guardband frequency between LTE carriers), andinband deployments (e.g., within an LTE carrier). Alternatively, it maybe possible to utilize a NB-IoT carrier in an unlicensed frequency band,e.g., in an OGRS context. In any of these possible deployment modes,NB-IoT carriers may include a variety of key features. For example,among various possible characteristics, NB-IoT carriers may supportflexible timelines for control and data channels; peak rates ofapproximately 20 kbps in the downlink and 60kbps in the uplink may besupported; single tone (e.g., 3.75 KHz vs. 15 KHz) and multi tone (15kHz) uplink modulation, using pi/2 binary phase shift keying or pi/4quadrature phase shift keying may be used (quadrature phase shift keyingmay also be used in the downlink); single antenna, half duplex frequencydivision duplexing may be used; and/or a per-UE carrier bandwidth of 180kHz may be used, according to some embodiments. Frequency hoppingfeatures for D2D communications may be supported. In some instances,NB-IoT carriers may provide coverage enhancement features for supportingcoverage up to 20 dB.

Any of a variety of features may be associated with an OGRS system,including when operating in regulated unlicensed spectrum, such as 900MHz unlicensed spectrum. For example, frequency hopping spread spectrum(FHSS) may be used. Channel carrier frequencies may be separated by aminimum of 25 kHz, or the 20 dB bandwidth of the hopping channel,whichever is greater. If the 20 dB bandwidth is less than 250 kHz (e.g.,as may be the case if NB-IoT carriers are used), the system may use atleast 50 channels. In this case, the average dwell time on a particularchannel may not exceed 400 ms within a 20 second period (e.g., dutycycle<=2%), and/or transmit power may be limited to 30 dBm. If the 20 dBbandwidth is 250 kHz or greater, then the system may use at least 25channels. In this case, the average dwell time may not exceed 400 mswithin a 10 second period (e.g., duty cycle<=4%), and/or transmit powermay be limited to 24 dBm. For example, the following table illustrates apossible set of specified features for OGRS operation depending on the20 dB bandwidth of the hopping channels used:

BW #Channel TX Power On Time Dwell Time <250 KHz >=50 30 dBm 400 ms 20sec >250 KHz >=25 24 dBm 400 ms 10 sec

Thus, if the 900 MHz unlicensed spectrum band (US ISM 900, 902-918 MHz)is used in conjunction with NB-IoT carriers (e.g., each having 200 kHzincluding guard bands), it may be possible to configure a pool of 80frequencies, as one exemplary possibility. In another configuration, apool of 130 frequencies spanning 902-928 MHz may be possible. Otherfrequency pools, e.g., having other numbers of frequencies available,are also possible. Various sets of those frequencies may be configuredas “scan channels” and “page channels”, which may be used for discoveryand/or other purposes, if desired.

One possible approach to providing synchronization within a D2Dcommunication framework may include a set of devices in a geographicalarea synchronizing to the symbol/subframe/frame timing and carrierfrequency provided by one of the devices, which may be referred to as asynchronization master, or in any of various other manners. Thisapproach may be similar in at least some ways to a cellular network inwhich wireless devices in a given area may camp on a base station.

However, such an approach may result in devices' coverage range beinglimited by the synchronization master's range, such that it may bepossible for two devices to not be able to communicate despite beingwithin communication range from each other if one is within the syncmaster's range and the other is out of the sync master's range. It mayalso be possible for two devices to be within communication range fromeach other, but to be synchronized to different sync masters withdifferent synchronization schemes.

Further, such an approach may result in an additional power consumptionburden upon the device selected to be the synchronization master, e.g.,since it may be expected to transmit synchronization reference signalsat a high power level to provide a maximum possible range for the D2Dcommunication group. Such a burden may be distributed among devices,e.g., by rotating the sync master position among devices, however, thismay introduce communication interruptions, extend discovery latencyamong devices, and/or require a more complex synchronization systemdesign in order to provide for event driven and/or periodic triggeredmaster/relay selection/re-selection/handover between different syncsources.

Still further, such a system may have a potentially substantiallikelihood for collisions during discovery, e.g., since many devices maysync to the same timing and frequency scheme provided by a sync master.

Accordingly, as a possible alternative, a D2D communication frameworkutilizing a synchronization scheme that does not rely on a sync masterdevice to provide synchronization signals for an entire D2Dcommunication group may be used, at least according to some embodimentsdescribed herein. For example, a preamble-based approach to performingsynchronization for narrowband D2D wireless communication may be used.FIG. 6 illustrates possible timing of various aspects of such anexemplary preamble based D2D communication framework, according to someembodiments.

According to such a framework, a discovery window may be preserved byeach wireless device for receiving synchronization sequences from otherdevices. Devices utilizing such a framework may refer to coordinateduniversal time (UTC) (e.g., as acquired via global navigationalsatellite system (GNSS) capability or in any of various other ways) oranother specified common reference clock to determine when eachdiscovery window occurs, at least according to some embodiments.

Each preamble transmission (which may include a synchronizationsequence) may be associated with device identification information, insome instances. For example, if a first device wants to establish a linkwith a second device, it may transmit a preamble including asynchronization sequence that is determined by and associated withidentification information for the first device. The preamble may befollowed by one or more other (e.g., discovery related) messages. Whenthe first device detects the presence of this preamble (e.g., that isassociated with identification information for the first device), thefirst device may continue to receive the following messages to proceedwith discovery and link establishment.

Additionally, or alternatively, in some instances (e.g., once linkestablishment has occurred), the synchronization sequence used duringpreamble transmission may be selected based at least in part on linkidentification information for a link associated with the preambletransmission. For example, once the first device and the second devicehave performed link establishment and established a link identifier forthe link between the first device and the second device, control and/ordata communications between the first device and the second device mayutilize a preamble that includes a synchronization sequence selectedbased at least in part on the link identifier.

As shown, the example framework of FIG. 6 illustrates an examplediscovery interval (602). Discovery intervals may occur periodically(e.g., according to a regular schedule/period, e.g., based on UTC time)and may thus allow for devices to periodically perform discovery andinitiate D2D communications. A discovery interval may begin with a sync(e.g., synchronization) preamble window (604) for a discovery receiver(DR) device. During the sync preamble window, a discovery initiator (DI)device may transmit a sync preamble (606). The sync preamble may includepart of the identification of the DR (e.g., DR ID) of a device that theDI intends to communicate with. In the case of presence discovery, thesync preamble may include part of the identification of acommon/presence ID, e.g., which may indicate that the DI will announceits presence so that all other devices (e.g., DRs) in range may be awareof its presence and availability for communication. Further, the syncpreamble may include all or part of a DI ID.

Following the sync preamble window, the DI and DR devices may wait for aperiod of time (msg 1 offset) (608). Then, the DI device may transmit afirst discovery message (msg 1) (610). As described above, the DI devicemay include some payload information in the message itself (e.g., viachannel coding) and may include some other payload information byselecting a subcarrier on which to send the message. The DR device maydetermine the content of the discovery message by decoding the channelcoded information and inferring the other information from thesubcarrier used.

Following the first discovery message, the DR device may respond (msg 2)(612). The devices may proceed with further communication during theremainder of the discovery interval and/or future intervals.

FIGS. 7-9—Discovery Message Design

FIGS. 7-9 illustrate discovery message design using subcarrier indexingto convey a portion of the payload information.

As shown in FIG. 7 , a discovery message payload of M bits may besubdivided into a first portion (e.g., K bits, e.g., corresponding to x)to be conveyed by subcarrier selection and a second portion (M−K bits)to be carried by channel coding. Note that the relative proportions of Kand M−K are illustrative only, and other relative sizes are possible. Asillustrated in FIG. 8 , the first portion of K bits may be an input to asubcarrier selection function, which may select a subcarrier (k_active)to be used to transmit the discovery message. The subcarrier selectionfunction may be expressed as k_active=f(x, u). As noted above, therelation between the number of available subcarriers (N) and K is givenby K=log₂(N), thus the more subcarriers are available, the moreinformation may be encoded via subcarrier selection. FIG. 9 illustratesa set of time/frequency resources available for the discovery messagetransmission. As shown, there may be 16 available subcarriers (e.g.,implying that K may be 4) and the message is transmitted on subcarrier 3(k_active). Thus, in the illustrated example, 4 bits (e.g., K=4) of thepayload of the discovery message and the remaining M−K=M−4 bits may betransmitted (e.g., via channel coding). Note that other numbers ofsubcarriers are possible.

Note that, although the techniques disclosed herein are primarilydescribed with respect to designing a discovery message, they could alsobe applied to other types of messages. Generally, any type of messagethat could be transmitted in different subcarriers could be designedaccording to the techniques herein, e.g., in order to convey someinformation through subcarrier selection. Similarly, these techniquescould also be applied in the time domain. In other words, a message thatcould be transmitted in any of multiple timeslots could use time slotselection (e.g., based on a slot index) in order to convey some of thepayload information. Further, these techniques could be applied moregenerally to selecting a specific set of time/frequency resources amongmultiple possible sets of time/frequency resources. For example, aportion of the payload of a message may be carried based on (e.g.,indicated by) a slot index and/or subcarrier index (or similartime/frequency indices) of the time/frequency resources used to carrythe message (or, potentially a different message).

FIGS. 10-13—Message Mapping Via Frequency Indexing for Peer-To-Peer(P2P) Discovery

FIGS. 10-13 illustrate examples and elements of possibledevice-to-device wireless communications using message mapping viafrequency indexing, e.g., in the case of peer-to-peer (P2P) discovery,according to some embodiments.

FIG. 10 illustrates a possible approach to generate synchronizationpreambles, e.g., particularly synchronization sequences, based on an ID(e.g., a DR ID and/or DI ID) and a frame number. For a given number ofavailable preamble sequences (S), the preamble may carry log2(S) bits ofthe ID. Thus, if N_(id) is the length of the ID expressed in binary,then floor(log2(S)) bits of the ID may be sent by preamble sequence,e.g., by detecting this particular sequence, the DR may knowfloor(log2(S)) bits in the ID. Further, floor(log2(K)) bits of the IDcan be sent by subcarrier indexing (e.g., of the discovery message, asdescribed above).

FIG. 11 illustrates a DR device monitoring for a sequence correspondingto its DR ID during a preamble detection window (e.g., sync preamblewindow, as described above with respect to FIG. 6 ). In response todetecting its local reference, e.g., sequence corresponding to its DR ID(e.g., in a desired sync preamble that describes part of the DR's DRID), the DR may determine a subcarrier (e.g., k_active=3) on which toreceive msg1 if the remainder of the DR ID were used to select thesubcarrier. Based on receiving the discovery message on that subcarrier,the DR may determine that the discovery message is intended for its DRID. Similarly, in the case illustrated by FIG. 12 , a DR may detect amatch to its local reference and determine a subcarrier. However, inthis case, the DR ID that the DI uses to select the subcarrier may be afalse alarm (e.g., a DR ID that shares the same preamble as the DR's DRID), and the DR may detect the false alarm by observing that thediscovery message is transmitted on a different subcarrier. In otherwords, a false alarm preamble (from the perspective of a specific DR)may be a preamble that could indicate its DR ID or at least one other DRID. The DR may be able to differentiate between a false alarm (e.g.,detecting a desired preamble followed by a discovery message on asubcarrier that does not correspond to its DR ID) and P2P discoverymessage intended for it (e.g., detecting the desired preamble followedby a discovery message on the subcarrier that does correspond to its DRID).

FIG. 13 illustrates five different cases for decoding the P2P discoverymessage, e.g., using the scenario of FIGS. 11-12 . For further detail,assume the following parameter values: N_(id)=16 bits, S=2¹³=8,192,N=2⁴=16. Note that these values are illustrative only, and that othervalues are possible. Also note that although 16 subcarriers are used inthe exemplary parameters, only 8 subcarriers are illustrated forconvenience.

The DR may operate as follows. If the DR does not detect a preamblesequence corresponding to its local reference, it may skip the msg1decoding. If the DR does detect a preamble sequence matching its localreference (which may be either desired/real or false alarm), it maymonitor to receive msg1 on the calculated subcarrier. If a successfulmsg1 is decoded, it may assume that the preamble is real and not a falsealarm, and it may interpret the bit fields of the msg1 accordingly. Ifno msg1 may be decoded correctly, it may determine that the preamble isa false alarm and discard the msg1. The criteria to determine successfuldecoding may be based on cyclic redundancy check (CRC) based on the DRID in the discovery message.

In case 1301, the DR may detect the discovery message on the subcarriercorresponding to its DR ID, e.g., subcarrier 3, as in FIG. 11 . In case1302, the DR may also detect the discovery message on the subcarriercorresponding to its DR ID, however in this case interference may alsooccur on a different subcarrier (e.g., subcarrier 5). This interferenceon subcarrier 5 may be discarded, e.g., because the DR may know that adiscovery message on any subcarrier other than subcarrier 3 is notrelevant to it. In case 1303, both a desired transmission (e.g., adiscovery message with the correct DR ID) and interference (e.g., someother transmission, such as a discovery message with a different DR ID)may occur on subcarrier 3. The DR may detect these transmissions, andmay or may not be able to successfully decode the discovery message withthe correct DR ID. In other words, the interference on subcarrier 3 maybe relevant because it may interfere with the DR's ability to decode thediscovery message intended for it. Case 1304 may be similar to case1303, with the addition of additional interference on subcarrier 5. Theadditional interference may not be relevant, e.g., because the DR candisregard this interference as it is not on subcarrier 3. In case 1305,the DR may detect interference on subcarrier 3, and may discard thistransmission, e.g., based on the CRC.

FIGS. 14-17—Message Mapping Via Frequency Indexing for PresenceDiscovery

FIGS. 14-17 provide additional information about presence discovery.Similar to FIGS. 11 and 12 , FIG. 14 illustrates a DR monitoring itslocal reference during a preamble detection window. However, in thiscase, it may detect a common presence preamble (e.g., which may beassociated with its local reference in addition to a preamble thatcorresponds to its DR ID). For example, in presence discovery, theentire presence ID may be associated with the preamble. Thus, allreceiving DRs may know based on the sync preamble that the discoverymessage is intended for all DRs. Therefore, the discovery message may beable to include other information, e.g., the DI ID. In some embodiments,the DR may only monitor a single subcarrier (e.g., as shown in FIG. 15), and thus no message payload may be offloaded based on subcarrierindexing. In some embodiments, e.g., as shown in FIG. 16 , the DR may beable to monitor all subcarriers, and thus information may be offloadedbased on subcarrier indexing. For example, floor(log2(K)) bits of the DIID, e.g., MSB or LSB may be offloaded. Alternatively, floor(log2(K))bits of other information associated with the discovery message payloadmay be offloaded.

FIG. 17 , similar to FIG. 13 , illustrates different cases for decodingthe presence discovery message, in the case that the DR is able to(e.g., allowed to) receive all available subcarriers at the same time(as in FIG. 16 ). Again, assume N=2⁴=16, however only 8 subcarriers areillustrated for convenience. Further, assume that 4 bits (e.g., MSB) ofDI ID is used to select the subcarrier of msg1 (e.g., an offloadedportion may be 4 bits). The DR may operate as follows: If the DR doesnot detect a preamble sequence corresponding to its local reference(e.g., the presence preamble sequence), it may skip the msg1 decoding.If the DR does detect the presence preamble (which may be eitherdesired/real or false alarm), it may monitor to receive msg1 on allavailable subcarriers. Thus, interference on all (e.g., any) availablesubcarriers may be relevant. If a successful msg1 is decoded on onesubcarrier, it may interpret the bits carried by the position (e.g.,subcarrier index) accordingly and may further decode and interpret thebit fields in the msg 1. If no msg1 may be decoded correctly, it maydetermine that the preamble is a false alarm and discard the msg1. Thecriteria to determine successful decoding may be based on CRC, e.g.,using the presence ID, in the discovery message.

In case 1701, the DR may detect the discovery message e.g., onsubcarrier 3. The DR may interpret the 4 bits of the MSB of the DI IDbased on the selection of subcarrier 3. Thus, the DR may know the entireDI ID based on the combination of the received (non-offloaded) portionof msg1 in combination with the identity of the subcarrier (e.g.,subcarrier 3). In case 1702, the DR may also detect the discoverymessage corresponding the common presence ID (illustrated in subcarrier3, but other subcarriers are possible), however in this caseinterference may also occur on a different subcarrier (e.g., subcarrier5). This interference on subcarrier 5 may be relevant, but may bediscarded, e.g., because it may not pass a CRC redundancy check (e.g.,it may not correspond to the common presence ID). In case 1703, both adesired transmission (e.g., a discovery message with the common presenceID) and interference (e.g., some other transmission, such as a P2Pdiscovery message with a different DR ID) may occur on subcarrier 3. TheDR may detect these transmissions, and may or may not be able tosuccessfully decode the discovery message with the common presence ID.Case 1704 may be similar to case 1703, with the addition of additionalinterference on subcarrier 5. The additional interference may also berelevant. In case 1705, the DR may detect interference on subcarrier 3,and may discard this transmission, e.g., based on the CRC.

FIGS. 18-19 Benefits of Offloading a Portion of a Message Via FrequencyIndexing

FIGS. 18 and 19 depict exemplary possible benefits of offloading aportion of a message via frequency indexing. In some embodiments, byreducing the amount of payload transmitted by channel coding, thedecoding performance may be improved due to a lower code rate. In otherwords, conveying some of the payload information via subcarrierselection allows a lower code rate to be used to transmit the remainingpayload information, e.g., given the same amount of time/frequencyresources. As shown, block error rate (BLER) increases as signal tonoise ratio (SNR) decreases. However, for lower code rates, the BLER isbetter (e.g., lower) for any given SNR. This effect may be observed inboth an EPA5Medium channel (FIG. 18 ) and an EPA5Low channel (FIG. 19 ).Note that the illustrated results are exemplary and other results may bepossible.

FIG. 20—Method of a Discovery Receiver (DR)

FIG. 20 illustrates an exemplary method of a discovery receiver (DR)monitoring a local reference. As shown, the DR may monitor one or moresubcarriers or channels for received signals (e.g., preambles) matchingits local reference during a sliding window (2010). In particular, inthe illustrated example, the device may monitor the one or moresubcarriers or channels for synchronization sequences 1, 2, and 3 (2020a-2020 c, respectively). Note that the device may monitor for any numberof synchronization sequences, according to some embodiments. In responseto detecting a preamble matching its local reference (2030 a-2030 c),the DR may calculate (e.g., determine) subcarrier and frequency indicesto monitor for a discovery message, e.g., msg1 (2040 a-2040 c). The DRmay receive a discovery message (2050), which may be associated with atleast one of the detected synchronization sequences. Note that more thanone discovery message may be received, according to some embodiments. Inresponse to successfully decoding the discovery message(s) (2060), theDR may determine the complete payload of the message (e.g., potentiallyincluding by determining an offloaded portion of the payload based onthe frequency index on which the message was received), and may replywith msg2 and continue the discovery process (2070).

FIG. 21—Design of a Discovery Message

FIG. 21 illustrates an exemplary design of a discovery message (e.g.,msg 1), according to some embodiments. As shown there may be 16available subcarriers, at a spacing of 3.75 KHz, among variouspossibilities. For example, there may be a total of 48 subcarriers at a180 KHz bandwidth, among various possibilities. In some embodiments, thediscovery message may have a duration of 16 ms. The 16 ms duration maycomprise 8 slots (e.g., each with a 2 ms duration), and each slot mayinclude 5 data symbols and 1 reference symbol (RS), among variouspossibilities. Thus, a total of 80 bits (e.g., 2 bits/data symbol*5 datasymbols/slot*8 slots=80 bits) may be available for transmission. In thecase of P2P discovery, for example, the payload of the discovery messagemay be a 16 bit DI ID, e.g., without a cyclic redundancy check (CRC).Therefore, the coding rate may be 0.2 (e.g., 16/80=0.2). In someembodiments, the DI ID may be uniquely mapped by the preamble sequenceand frequency/subcarrier index. For example, if 4 bits of the DI ID areoffloaded, the coding rate may be 0.15 (e.g., (16−4)/80=0.15).Similarly, in the case of presence discovery, the payload may be a 16bit DR ID (e.g., a common/presence ID), which may similarly be offloadedbased on frequency indexing. Such mapping (e.g., offloading) may allowfor a lower coding rate to be used for the discovery message. Decodingof the DI (e.g., or DR) ID in the message may be validated, e.g., by afriend-list check. In other words, the receiver may compare the decodedID to a list of expected (e.g., possible) IDs for validation. In someembodiments, the discovery message may be transmitted using quadraturephase shift keying (QPSK) and LTE tail-biting convolutional code (TBCC).Other types of channel coding (e.g., polar coding, turbo coding, etc.)may also be used.

FIG. 22—Process for Transmitting and Receiving a Message

FIG. 22 is a flow chart depicting an exemplary process for transmittingand receiving a message, e.g., the discovery message of FIG. 21 . Thisexemplary process may be consistent, e.g., broadly speaking, with thesimulation results portrayed in FIGS. 25-53 and discussed below. Notethat several of FIGS. 25-53 may include various deviations, e.g., invarious details, from the exemplary process.

Aspects of the method of FIG. 22 may be implemented by a wirelessdevice, such as the UEs 106 illustrated in and described with respect toFIGS. 1-3 , or more generally in conjunction with any of the computersystems or devices shown in the Figures, among other devices, asdesired. Note that while at least some elements of the method aredescribed in a manner relating to the use of communication techniquesand/or features associated with 3GPP specification documents, suchdescription is not intended to be limiting to the disclosure, andaspects of the method may be used in any suitable wireless communicationsystem, as desired. In various embodiments, some of the elements of themethods shown may be performed concurrently, in a different order thanshown, may be substituted for by other method elements, or may beomitted. Additional method elements may also be performed as desired.For example, a processor (and/or other hardware) of a device may beconfigured to cause the device to perform any combination of theillustrated method elements and/or other method elements. As shown, themethod may operate as follows.

In some embodiments, a payload may be encoded using TBCC (or othercoder), e.g., by a DI device. The encoded payload may be rate matchedand modulated. Symbols may be generated for a carrier (e.g., or multiplecarriers). The symbols may be transmitted (e.g., by the DI device) on achannel.

The symbols may be received and downsampled (e.g., by a DR device) fromthe channel. The DR device may perform frequency and/or time refinementand may perform channel estimation (e.g., minimum mean squared error(MMSE)). The received signal may be equalized (e.g., maximum-ratiocombining (MRC)), demodulated, de-rate matched, and decoded. The decodedpayload may be interpreted by the DR device (e.g., ID information fromthe payload may be determined).

FIG. 23—Single Slot vs Cross Slot Channel Estimation

FIG. 23 illustrates single slot vs cross slot channel estimationtechniques. Channel estimation may be a significant factor for decodingperformance. As shown, in cross slot channel estimation, multiplereference symbols (RS) may be used to estimate the channel. However, insingle slot channel estimation, only a single reference symbol may beused. With single slot MMSE channel estimation, RS may have the same SNRas data symbol, and thus may degrade the performance. With cross-slotMMSE channel estimation, SNR of RS may be significantly improved (e.g.,depending on Doppler spread) and thus may improve the decodingperformance.

FIG. 24—Reference Signal

FIG. 24 illustrates received RS, e.g., as may be used for carrierfrequency refinement (e.g., CFO refinement). Denote received signal atRS symbol k as s_k, then angle(conj(s_(k−1))*s_k) may be equal to2*pi*F_(error)*T_(delta), where F_(error) is carrier frequency residualerror, and T_(delta) is the time delta between two adjacent DMRS symbol.

In some embodiments, single tap CFO refinement may be performed asfollows. A sum may be calculated over different DMRS, e.g.,:P1=sum_k(conj(s_(k−1))*s_k) for each of the antenna signal. P1 may besummed over the two antennas. F_(error) may be estimated as:F_(error)_est=angle(P1_sum)/(2*pi*T_(delta)).

In some embodiments, multiple-tap CFO refinement may be performed asfollows. A sum may be calculated over different DMRS with differentlags: Pi=sum_k (conj(s_(k−i))*s_k) for each of the antenna signal, wherei=1 to 4. Pi may be summed over the two antennas, where i=1 to 4. Pi maybe combined (e.g., and weighted), e.g.,: P=sum(w_i*Pi), where w_i isfilter coefficient can be optimized. F_(error) may be estimated, e.g.,F_(error_est)=angle(P)/(2*pi*T_(delta)).

FIGS. 25-53

FIGS. 25-28 illustrate exemplary simulated results, e.g., estimates ofblock error rate (BLER) as a function of signal-to-noise ratio (SNR) forvarious code rates, e.g., using different channel models. FIG. 25illustrates the results using an additive white Gaussian noise (AWGN)channel model. FIG. 26 uses an Extended Pedestrian A (EPA) 5 low model.FIG. 27 uses an EPA 5 medium model. FIG. 28 uses an Extended Vehicular A(EVA) 30 low model.

FIGS. 29-32 illustrate further exemplary simulated results, includingthe effect of carrier frequency offset (CFO) estimation. The CFOresidual may be uniformly distributed (e.g., [−max CFO, +max CFO]).There may be degradation with residual error in CFO refinement. Thesefigures use the same channel models as FIGS. 25-28 .

FIGS. 33 and 34 illustrate further exemplary simulated results, usingpolar coding techniques. FIG. 33 may use the AWGN model and FIG. 34 mayuse the EPA 5 low model.

FIG. 35 illustrates the effects of single slot channel estimation. FIG.35 may be compared to FIG. 33 , e.g., which uses cross slot channelestimation for the same simulation. Notably, the results illustrated inFIG. 35 may represent approximately a 4 dB loss relative to the resultsof FIG. 33 .

FIGS. 36 and 37 illustrate further exemplary simulated results,including the effect of different levels of CFO refinement. Asillustrated, without CFO refinement, BLER may be limited by an errorfloor and multi-tap may provide a significant gain over single tap.Further optimization may be possible, e.g., via one or more of: maximumratio combining of Rx signal (instead of equal gain combining) oroptimizing filter coefficients.

FIGS. 38-43 illustrate further exemplary simulated results, showing thecarrier frequency residual error of different CFO schemes, at variousSNRs using different channel models. The simulated results may suggest aconsistent CFO estimation error (e.g., error may not depend on initialmaximum CFO). FIGS. 38 and 39 use the AWGN model at SNR equal to 0 or 8,respectively. FIGS. 40 and 41 use the EPA 5 low model at SNR equal to 0or 8, respectively. FIGS. 42 and 43 use the EPA 5 medium model at SNRequal to 0 or 8, respectively. FIGS. 44 and 45 use the EVA 30 low modelat SNR equal to 0 or 8, respectively.

FIGS. 46-53 illustrate further exemplary simulated results, showing theimprovements (e.g., pull-in range) of CFO refinement. FIGS. 46 and 47use AWGN. FIGS. 48 and 49 use EPA 5 low. FIGS. 50 and 51 use EPA 5medium. FIGS. 52 and 53 use EVA 30 low. Collectively, these results maysuggest a pull-in range of approximately 250 Hz, e.g., for each of themodels.

FIGS. 54 and 55—Exemplary Mapping Scheme and Additional Information

FIG. 54 illustrates a table of a 4-bit field and slot index. As shown,if an index describes 16 possible slots, up to 4-bits of information maybe offloaded (e.g., 2{circumflex over ( )}4=16).

FIG. 55 illustrates that, if a message is transmitted using one of theslots (e.g., slot 1, in the illustrated example), the 4-bits of themessage payload can be determined based on the slot index (e.g., usingthe table of FIG. 54 ). In the illustrated example, slot 1 correspondsto a message payload of “0001”.

It will be appreciated that the example of FIGS. 54 and 55 isillustrative only. The index may be a frequency index, a time index(e.g., denominated in symbols, milliseconds, or other units of time inaddition to slots), or a combined time and frequency index. Similarly,other numbers of index values may allow offloading of different amountsof payload (e.g., a different length bit field). For example, 32possible index values could offload 5 bits of message payload (e.g., a5-bit field) because 2{circumflex over ( )}5=32. Further, the example ofFIGS. 54 and 55 could apply to discovery messaging and/or to other typesof messages.

It is well understood that the use of personally identifiableinformation should follow privacy policies and practices that aregenerally recognized as meeting or exceeding industry or governmentalrequirements for maintaining the privacy of users. In particular,personally identifiable information data should be managed and handledso as to minimize risks of unintentional or unauthorized access or use,and the nature of authorized use should be clearly indicated to users.

In addition to the above-described exemplary embodiments, furtherembodiments of the present disclosure may be realized in any of variousforms. For example, some embodiments may be realized as acomputer-implemented method, a computer-readable memory medium, or acomputer system. Other embodiments may be realized using one or morecustom-designed hardware devices such as ASICs. Still other embodimentsmay be realized using one or more programmable hardware elements such asFPGAs.

In some embodiments, a non-transitory computer-readable memory mediummay be configured so that it stores program instructions and/or data,where the program instructions, if executed by a computer system, causethe computer system to perform a method, e.g., any of the methodembodiments described herein, or, any combination of the methodembodiments described herein, or, any subset of any of the methodembodiments described herein, or, any combination of such subsets.

In some embodiments, a device (e.g., a UE 106 or 107) may be configuredto include a processor (or a set of processors) and a memory medium,where the memory medium stores program instructions, where the processoris configured to read and execute the program instructions from thememory medium, where the program instructions are executable toimplement any of the various method embodiments described herein (or,any combination of the method embodiments described herein, or, anysubset of any of the method embodiments described herein, or, anycombination of such subsets). The device may be realized in any ofvarious forms.

Although the embodiments above have been described in considerabledetail, numerous variations and modifications will become apparent tothose skilled in the art once the above disclosure is fully appreciated.It is intended that the following claims be interpreted to embrace allsuch variations and modifications.

What is claimed is:
 1. An apparatus, comprising: a processor configuredto cause a first wireless device to: subdivide an identifier into afirst portion of the identifier and a second portion of the identifier;transmit a sequence, including the first portion of the identifier, to asecond wireless device; generate a payload, including a non-offloadedpart of the second portion of the identifier; select, based on anoffloaded part of the second portion of the identifier, a resource froma plurality of available resources, wherein the resource comprises animplicit indication of the offloaded part of the second portion of theidentifier; and transmit the payload on the resource to the secondwireless device, wherein the payload and the implicit indication of theoffloaded part of the second portion of the identifier are useable todetermine the second portion of identifier.
 2. The apparatus of claim 1,wherein the identifier includes a receiver identifier.
 3. The apparatusof claim 1, wherein the identifier includes an initiator identifier. 4.The apparatus of claim 1, wherein the resource is selected further basedon a frame number.
 5. The apparatus of claim 1, wherein the resource isselected further based on a value of prior known information.
 6. Theapparatus of claim 1, wherein the payload includes at least one bit thatis not part of the identifier, wherein the resource comprises animplicit indication of the at least one bit that is not part of theidentifier.
 7. A second wireless device, comprising: a radio; and aprocessor configured to cause the second wireless device to: receive asynchronization preamble, including a first portion of an identifier,from a first wireless device; determine at least one resource to monitorduring a subsequent time window, wherein the at least one resource isselected from a plurality of available resources; receive a message on afirst resource of the at least one resource during the subsequent timewindow, wherein the message includes a non-offloaded part of a secondportion of the identifier; determine an offloaded part of the secondportion of the identifier based at least in part on an identity of thefirst resource, wherein the offloaded part of the second portion of theidentifier is not explicitly included in the message; and determine acomplete identifier, wherein the complete identifier includes thenon-offloaded part of the second portion of the identifier and theoffloaded part of the second portion of the identifier.
 8. The secondwireless device of claim 7, wherein the synchronization preamble isreceived during a synchronization preamble window, wherein the messageincludes a device to device discovery message.
 9. The second wirelessdevice of claim 7, wherein the synchronization preamble indicates atleast one of: identification information for the first wireless device;identification information for the second wireless device; or a commonpresence identifier.
 10. The second wireless device of claim 7, whereinthe at least one resource includes only the first resource.
 11. Thesecond wireless device of claim 10, wherein the first resource comprisesa single subcarrier associated with the identifier.
 12. The secondwireless device of claim 11, wherein the identifier is a recipientidentifier of the second wireless device.
 13. The second wireless deviceof claim 11, wherein the identifier is a common presence identifier. 14.The second wireless device of claim 7, wherein the synchronizationpreamble includes a common presence identifier, wherein the at least oneresource includes all resources of the plurality of available resources.15. The second wireless device of claim 7, wherein the identifierincludes a receiver identifier.
 16. A method, comprising: at a secondwireless device: receiving a synchronization preamble, including a firstportion of an identifier, from a first wireless device; determining atleast one resource to monitor during a subsequent time window, whereinthe at least one resource is selected from a plurality of availableresources; receiving a message on a first resource of the at least oneresource during the subsequent time window, wherein the message includesa non-offloaded part of a second portion of the identifier; determiningan offloaded part of the second portion of the identifier based at leastin part on an identity of the first resource, wherein the offloaded partof the second portion of the identifier is not explicitly included inthe message; and determining a complete identifier, wherein the completeidentifier includes the non-offloaded part of the second portion of theidentifier and the offloaded part of the second portion of theidentifier.
 17. The method of claim 16, wherein the synchronizationpreamble is received during a synchronization preamble window, whereinthe message includes a device to device discovery message.
 18. Themethod of claim 16, wherein the synchronization preamble indicates atleast one of: identification information for the first wireless device;identification information for the second wireless device; or a commonpresence identifier.
 19. The method of claim 16, wherein the at leastone resource includes only the first resource.
 20. The method of claim16, wherein the first resource comprises a single subcarrier associatedwith the identifier.